Compensating device for a tool unit and fitting method by means of the tool unit

ABSTRACT

A compensating device for a tool for fitting an element into a hole of a workpiece, the tool mounted axially on a housing by the compensating device, the compensating device having a clamping arrangement arranged between the tool and the housing and including at least two controllable clamping units. The clamping units are operable in an initial state to secure the tool rigidly to the housing, and in a compensating state to set different degrees of freedom defining possibilities of movement of the tool, and the compensating device also includes a control unit which is designed to activate the clamping units.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of PCT/EP2014/052182, filed Feb. 5, 2014 which claims priority from German Patent Application No. DE102013002863.9, filed Feb. 20, 2013, the disclosures of which are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

The present invention relates to a compensating device for a tool unit for fitting an element into a hole of a workpiece.

Furthermore, the present invention relates to a method for the automated fitting of an element into a hole of a workpiece with the aid of the tool unit.

Furthermore, the present invention relates to a tool unit having a compensating device of this type.

A tool unit is understood in the present context to mean, in particular, a setting unit for the setting of, for example, blind rivets, a screw unit for screwing in a screw element or other press-in or fit-in units for fitting a fitting element. The tool unit serves for introducing the fitting elements into corresponding bores of the workpiece.

For example, in a blind riveting method, two workpieces, usually two metal sheets, are connected to one another, in that a blind rivet which has a rivet head and a rivet shank is inserted from one side through a bore in the workpieces. The riveted joint is made by drawing out the shank opposite to the insertion direction. An enlarged end of the rivet shank thereby deforms a part of the blind rivet which projects on the rear side. The stem of the shank breaks off at a predetermined breaking point as soon as a specific tensile force is overshot,

To make such blind riveted joints, hydraulically, electrically, or pneumatically operating blind riveting tools are known. Blind rivets are also increasingly used in the motor vehicle sector for the connection of components which have hitherto been connected to one another, for example, by welding. Since motor vehicle manufacture is automated to a high degree, the connection of body components is carried out for the most part with the aid of industrial robots. The industrial robots are equipped for this purpose with a special tool unit serving for holding the fitting element/blind rivet. The blind rivets are provided by a singling-out device and delivered to the tool unit in an automated way. The industrial robot subsequently moves to the position of the bore in the workpieces and fits the blind rivet. Owing to deviations in the position of the tool unit on the industrial robot or to component tolerances of the workpieces, undesirable deviations in the relative position between the respective fitting element and the bore may occur. Moreover, the industrial robot also may have inaccuracies when moving to a predetermined desired position.

Such deviations in position, when a tool unit is mounted rigidly on the industrial robot, lead, for example, to obliquely set rivet elements in the component bores and thus give rise to faulty rivetings. In the case of rivet elements which are additionally intended to assume a sealing-off function, an oblique orientation of the rivet head in relation to the workpieces causes a leak in the manufactured component. On account of this, incorrectly positioned or set rivet elements have to be remachined in a complicated way. Furthermore, in the event of deviations in position, inadmissible transverse forces also arise on the tool unit during the fitting of the rivet element and may lead to increased wear or even to destruction of mechanical structural elements of the tool unit.

For a high-quality fitted connection which is also reliable in the long term, it is necessary for the fitting element to be oriented axially parallel to a through bore, into which the fitting element is inserted for the connection of at least two components. Since the tool unit is mounted on a robot arm of the industrial robot for an automated fitting process, it is necessary to compensate the deviations in position (deviations of the fitting element in a plane parallel to the workpiece surface) and deviations in attitude (angular errors in the axial axes of the fitting element in relation to the axial axis of the bore in the workpiece).

In the field of fitting technology, therefore, systems are known which allow tolerance compensation in a plane perpendicular to the fitting direction by means of a flexible suspension of the fitting tool or tool unit. For example, WO 2006/063629 describes a compensating unit for a tool unit, by means of which an element, for example a component or a fitting element, can be mounted in a workpiece. In this case, the tool unit is fastened, via a bearing designed as a pendulum or pivoting bearing, on a compensating element designed as a sliding plate. The bearing allows a tilting movement about the axial direction of the fitting element and therefore also in relation to the sliding plate. The sliding plate itself is held between two guide walls so as to be displaceable perpendicularly to the axial direction in an x-y plane. However, on account of the freely movable bearing, the tool unit cannot be secured to the robot arm while the robot arm is moving to the fitting position. Consequently, especially when the robot is stopped suddenly, the tool unit can be only insufficiently secured mechanically. Since the possibility of controlling the tilting movement is lacking, the compensating unit described can be operated only in a fitting position tilted vertically downwards. In other fitting positions (for example, a horizontal position of the tool unit), the tool unit tilts automatically into a constrained position on account of the force of its weight. The fitting element can therefore no longer be positioned correctly on the workpiece. Moreover, in these other fitting positions, simply the dead weight of the tool unit causes deflection of the sliding plate. This, in turn, is detrimental to the tolerance compensation of the compensating unit described. Furthermore, because of the numerous mechanical compensating elements, the compensating unit has a complex set-up and is therefore susceptible to faults. Moreover, the mechanical compensating elements are subject to natural wear which results in poorer tolerance compensation after a certain period of use.

BRIEF SUMMARY OF THE INVENTION

The object on which the invention is based is, therefore, to specify an improved compensating device for a tool unit and a tool unit which allows the automated fitting of an element, in particular of a fitting element, into a workpiece. Furthermore, an object of the invention is to specify an improved method for the automated fitting of an element into a bore of a workpiece.

The above object is achieved by means of a compensating device for a tool unit for fitting an element into a workpiece, the tool unit being mounted, oriented in an axial direction, on a housing by means of the compensating device, the compensating device having a clamping arrangement arranged between the tool unit and the housing, with at least two controllable clamping units which are designed, in an initial state of the clamping arrangement, to secure the tool unit essentially rigidly to the housing and, in a compensating state of the clamping arrangement, to set different degrees of freedom of the tool unit, the degrees of freedom defining possibilities of movement of the tool unit, and, furthermore, the compensating device having a control unit which is designed to activate the clamping units.

The above object is achieved, furthermore, by means of a method for the automated fitting of an element into a hole of a workpiece with the aid of a tool unit which is mounted, oriented in an axial direction, on a housing by means of a compensating device, in particular a compensating device of the abovementioned type, the compensating device having a clamping arrangement with at least two controllable clamping units, and the method having the steps:

-   -   setting of an initial state of the clamping arrangement, so that         the tool unit is secured essentially rigidly to the housing,     -   automated feeding of the tool unit to the hole,     -   setting of a first degree of freedom for the tool unit by means         of at least one of the clamping units,     -   introduction of the element into the hole,     -   execution of a fitting process in order to fit the element into         the hole, a second degree of freedom which deviates from the         first degree of freedom being set for the tool unit by means of         at least one of the clamping units before and/or during the         fitting process, and the degrees of freedom defining         possibilities of movement of the tool unit.

Furthermore, the above object is achieved by means of a tool unit having a compensating device of the abovementioned type.

The tool unit may be, in particular, a fitting tool for carrying out a blind riveting method, in which two or more workpieces are connected to one another, in that a blind rivet is inserted from one side through a bore in the workpieces. The tool unit may likewise be used for what is known as stud welding, in which the workpieces are connected with the aid of a fitting stud. However, the compensating device according to the invention can also be used, moreover, for any other tool units for fitting a fitting element.

In the compensating device according to the invention, the clamping units can be activated in such a way that, in an initial state of the clamping arrangement, the tool unit is secured rigidly to the housing and is oriented essentially in the axial direction. This makes it possible to lock the tool unit reliably on the housing which is connected, for example, to a robot arm, while the fitting element is pivoted into the intended fitting position. The tool unit is thus held reliably on the housing, for example, even in the event of an emergency switch-off of the robot (which guides the tool unit). Damage caused, for example, by the tool unit knocking against the housing after an abrupt stop of the robot, can be avoided.

Furthermore, the compensating device according to the invention allows a controlled enabling of different degrees of freedom of the tool unit. For example, the clamping units can firstly be activated such that, to compensate the attitude of the tool unit, only a tilting movement of the tool unit in relation to the axial direction is enabled. Alternatively, the tool unit may initially have only one possibility of movement in the axial direction. Depending on specific conditions, the clamping arrangement may be activated such that additional and/or alternative possibilities of movement are set on the tool unit. Thus, for example, a lateral movement of the tool unit perpendicularly to the axial direction may also be made possible.

Moreover, there is the possibility of activating the clamping units such that the enabling of the possibilities of movement takes place (slowly) as a function of predetermined conditions and/or according to a predetermined profile. In other words, the possibilities of movement are not necessarily enabled digitally or abruptly. For example, the possibilities of movement may also be set as a function of the size of the offset in position between the fitting element and the bore in the workpieces to be connected. This leads to a more accurate introduction of the fitting element into the bore provided and therefore to a more reliable fitted connection between the workpieces. On account of the correct orientation of the fitting element in relation to the workpieces, a possible sealing function of the fitted connection can also be fulfilled reliably.

Further, in the proposed compensating device, the same elements (the controllable clamping units) are used for enabling and for securing the tool unit. This results in a technically simple and therefore reliable implementation of the compensating device.

The object is thus achieved in full.

In the compensating device according to the invention, it is especially advantageous if the clamping units are arranged so as to be offset to one another in the axial direction.

By virtue of this measure, the degree of freedom and the corresponding possibilities of movement of the tool unit can be set precisely. Thus, for example, a tilting movement on the tool unit in relation to the axial direction can be enabled by means of one of the clamping units. This allows angular compensation of the fitting element in relation to the axial axis of the hole in the workpiece. With the aid of corresponding activation of the second clamping unit, for example, compensation of the position of the tool unit in an x-y plane parallel to the workpiece surface can additionally take place. Since the clamping units are offset axially to one another, the enabling of the possibilities of movement can be adapted especially effectively to the offset in position prevailing between the fitting element and the bore.

Furthermore, it is preferable if at least one of the clamping units surrounds the tool unit in a circumferential direction transversely to the axial direction.

In this embodiment, the at least one clamping unit preferably bears directly against the tool unit. In this case, the tool unit is surrounded in an axial portion preferably completely by the clamping unit. For example, the clamping unit may be designed such that an inside diameter of the clamping unit can be varied as a function of activation. The tool unit can thereby be secured or enabled directly by means of the clamping unit. Consequently, complicated structural solutions which are arranged between the clamping unit and the tool unit may be dispensed with. Moreover, this results in a small overall size of the compensating device both in the radial and in the axial direction.

According to a further embodiment, at least one of the clamping units has a compressed-air hose.

In this preferred embodiment, for example, a bellows-type cylinder may be used as the clamping unit. This makes it possible to implement the clamping unit in a technically simple and reliable way. Furthermore, the compensating device has high stability, since clamping units of this type have lower wear than mechanical compensating or locking mechanisms.

In a further embodiment, at least one of the clamping units has a plurality of clamping elements which are arranged so as to be offset to one another in the circumferential direction.

As a result of such an arrangement of clamping elements, for example, only one special possibility of lateral movement of the tool unit may be enabled in a directed way. This may be implemented, for example, in that all the clamping elements, with the exception of one clamping element, remain in the initial state of the clamping arrangement, the one clamping element enabling, as the possibility of movement of the tool unit, that direction in which the clamping element is arranged. Furthermore, the plurality of clamping elements leads to increased fail-safety of the clamping unit. In other words, for example even in the event of failure of a clamping element, a restricted clamping action can still always be exerted upon the tool unit.

According to a further embodiment, the plurality of clamping elements has a compressed-air hose and/or a clamping cylinder.

In this embodiment, the clamping elements may be designed, for example, as axially running hose pieces which bear directly against the tool unit. Preferably, for example, three hose pieces running in the axial direction are arranged on the tool unit and have in each case an angular offset of 120° with respect to one another. In an alternative embodiment, any other number of hose pieces may also be arranged on the tool unit. Furthermore, there is the possibility of exerting the clamping action upon the tool unit also by means of clamping cylinders which act directly upon the tool unit. Moreover, the clamping cylinders may also have clamping jaws which bear against the tool unit and partially surround this in the circumferential direction. With the aid of these clamping elements, the clamping arrangement and consequently the compensating device can be implemented in a technically simple and reliable way.

In a further embodiment, the compensating device has, furthermore, an inner housing which is arranged between the tool unit and the housing, one of the two clamping units being arranged between the tool unit and the inner housing and the other of the clamping units being arranged between the inner housing and the housing.

This embodiment provides, in particular, a compensating mechanism in which attitude compensation (angular error) and position compensation (deviations in the x-y plane parallel to the workpiece surface) can be activated essentially independently of one another.

In a further embodiment, the compensating device has, furthermore, a rubber damper which is secured to the housing and on which the tool unit is mounted elastically.

By virtue of this measure, the tool unit can be mounted in such a way that the clamping arrangement is essentially relieved of holding forces for securing the tool unit in the fitting direction along the axial direction, but a compensating movement of the tool unit is nevertheless made possible. The clamping arrangement can therefore be aimed mainly at implementing the compensating function.

In a further embodiment, the compensating device has, furthermore, a mechanical guide element on which the tool unit is mounted rotatably and/or displaceably.

In this case, the guide element may be arranged on the housing and/or the inner housing. Moreover, the mechanical guide elements may have plain bearings and/or rolling bearings (for example, ball bearings). The guide elements may be, for example, of conical form. With the aid of the guide elements, the clamping arrangement is relieved of the dead weight of the tool unit and can therefore be optimized for implementing a compensating function.

According to a further embodiment, the compensating device has, furthermore, an angular position transmitter unit which is designed to detect an angular position of the tool unit in three-dimensional space, the control unit being coupled electrically to the angular position transmitter unit and being designed to activate the clamping units on the basis of the angular position.

With the aid of the angular position transmitter unit, compensation of the dead weight of the tool unit can take place. For example, the enabling range of the compensating device can be set as a function of the angular position. Consequently, by means of the compensating device, good tolerance compensation is achieved in any desired position of the tool unit. In other words, by the angular position being taken into account, any desired position of use of the tool unit becomes possible.

According to a further embodiment, the compensating device has, furthermore, a first force detection unit which is designed to detect an, in particular, axial fitting force which is exerted upon the element by the tool unit in order to fit the element, the control unit being coupled electrically to the first force detection unit and being designed to activate the clamping units on the basis of the fitting force.

For example, the first force detection unit may have a load cell which detects the tensile force on the blind rivet during the fitting process. With the aid of the tensile force, there is the possibility of monitoring the time sequence of the fitting process. The degree of freedom or the possibilities of movement of the tool unit can thus be set as a function of the tensile force or of the time sequence of this fitting process. The fitting element is consequently positioned precisely in the bore and a reliable fitted connection is made.

According to a further embodiment, the compensating device has, furthermore, a second force detection unit which is arranged between the tool unit and the housing and which is designed to detect a deflecting force which is oriented, in particular, transversely to the axial direction and which, when the element is being fitted into the workpiece, is exerted upon the element by the workpiece on account of an offset in position between the element and the hole, the control unit being coupled electrically to the second force detection unit and being designed to activate the clamping units on the basis of the deflecting force.

The second force detection unit may have, for example, strain gauges which are arranged between the tool unit and the housing. With the aid of the strain gauges, the deflecting force which results directly from the offset in position or offset in attitude between the fitting element and the bore of the workpiece is detected. The clamping units can consequently be activated very precisely as a function of the currently detected offset. The possibilities of movement of the tool unit are therefore not enabled digitally (tool unit secured or freely movable), but instead enabling can be adapted continuously to the requirements on the basis of the detected offset. This results in high-quality fitted connections which are reliable in the long term.

According to a further embodiment, a maximum deflecting movement of the tool unit in the direction of the possibilities of movement can be defined by means of the clamping units.

For example, the maximum deflecting movement of the tool unit can be set with the aid of the pressure inside a bellows-type cylinder. In this case, the size of the deflecting movement may also be determined, for example, as a function of the detected axial fitting force and/or of the detected deflecting force. Furthermore, the angular position determined can also be included in the determination of the maximum deflecting movement. In this embodiment, therefore, the extent of the possibilities of movement (or the maximum deflection in the direction of the possibilities of movement) is also enabled in a controlled or regulated way.

According to an especially preferred embodiment of the method according to the invention, an angular position of the tool unit in three-dimensional space is detected, the clamping units being activated on the basis of the angular position.

The detected angular position is in this case taken into account, in particular, in the setting of the first and/or of the second degree of freedom or in the setting of the possibilities of movement resulting from this. The enabling range of the tool unit can thus be defined as a function of position. The dead weight of the tool unit is compensated independently of the position of use of the tool unit. The method according to the invention consequently allows reliable fitted connections to be made independently of the position of use of the tool unit.

According to a further embodiment of the method, during the fitting process an, in particular, axial fitting force is detected which is exerted upon the element by the tool unit in order to fit the element, the clamping units being activated on the basis of the fitting force in order to set the possibilities of movement of the second degree of freedom.

For example, in blind riveting, a tensile force on the rivet can be measured during the fitting process. As soon as the measured force rises, for example, a further possibility of movement of the tool unit is enabled by means of the clamping units as a function of the detected tensile force. The tool can consequently be oriented slowly toward the component during the fitting process. A high-quality fitted connection is consequently made.

In a further embodiment of the method according to the invention, during the fitting process a deflecting force is detected which is oriented, in particular, transversely to the axial direction and which is exerted upon the element by the workpiece during the fitting of the element into the workpiece on account of an offset in position between the element and the hole, the clamping units being activated on the basis of the deflecting force in order to set the possibilities of movement of the second degree of freedom.

In this embodiment, the deflecting force which results directly from the offset in position/angular offset of the fitting element in relation to the bore in the workpiece is detected. The clamping units can thus be activated individually on the basis of the offset during the prevailing fitting process. Consequently, in each case the highest possible quality can be ensured when the fitting element has been fitted.

Furthermore, there is the possibility of activating the clamping units as a function of the detected tensile force and of the detected deflecting force. In this embodiment, the possibilities of movement of the tool unit can be set both on the basis of the progress of the fitting process and as a function of the transverse forces/deflecting forces actually occurring.

According to a further embodiment, the initial state of the clamping arrangement is set during the fitting process or after the fitting process.

If the initial state (for example, completely filled bellows-type cylinder) is restored during the fitting process, a force is consequently exerted, for example, upon a robot arm coupled to the tool unit. The robot arm can therefore track the current fitting position and this new position can be stored in the robot. The subsequent fitting process is thereby optimized and accelerated.

According to a preferred embodiment of the tool unit, the tool unit has the first force detection unit which is designed to detect an, in particular, axial fitting force which is exerted upon the element by the tool unit in order to fit the element, the control unit being coupled electrically to the first force detection unit and being designed to activate the clamping units on the basis of the fitting force.

For example, the first force detection unit may have a load cell which detects the tensile force at the blind rivet during the fitting process. In this embodiment, the first force detection unit may be arranged, for example, outside the compensating device and on the tool unit.

It would be appreciated that the features mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or alone, without departing from the scope of the present invention.

Moreover, the features, properties and advantages of the compensating device according to the invention can also be applied correspondingly to the method according to the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention is explained in detail below with reference to the exemplary, but not limiting, embodiments that are shown in the drawings, in which:

FIG. 1 shows a diagrammatic illustration of an industrial robot with a fitting arrangement which has a tool unit and a compensating device.

FIGS. 2A-2C shows an embodiment of the compensating device according to the invention in, respectively, an initial state, a first compensating state, and a second compensating state.

FIG. 3 shows a first embodiment of the method according to the invention.

FIG. 4 shows a second embodiment of the method according to the invention.

FIG. 5 shows a diagrammatic illustration of a force detection unit for detecting a deflecting force.

FIGS. 6A-6F each show a vertical cross section of one of six further alternative embodiments of the compensating device according to the invention.

FIG. 7A shows a top view of a still further alternative embodiment of the compensating device according to the invention.

FIG. 7B shows a side view in partial vertical cross section of the compensating device according to FIG. 7A.

FIG. 8 shows a top view in partial horizontal cross section of still another alternative embodiment of the compensating device according to the invention.

FIG. 9 show a top view in partial horizontal cross section of a further embodiment of the compensating device according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates an industrial robot 10 with a fitting arrangement 12. In this case, the fitting arrangement 12 is mounted movably on a robot arm 14 of the robot 10. The fitting arrangement 12 has a tool unit 16 which is mounted, oriented in an axial direction 19, on a housing 20 of the fitting arrangement 12 via a compensating device 18. In the present exemplary embodiment, the tool unit 16 is designed as a blind riveting tool 16 and serves for fitting a blind rivet 22 into a bore 24 in order to connect a first and a second workpiece 26, 28 to one another.

The robot 10 is designed to insert the blind rivet elements 22 in an automated way. For this purpose, the fitting arrangement 12 has, furthermore, a delivery unit 30 which is connected to a singling-out device 31, not illustrated in FIG. 1, and which allows the automated provision of blind rivet elements 22.

According to an automated blind riveting method, a blind rivet 22 is provided by the delivery unit 30 and is picked up by a mouthpiece 32 of the blind riveting tool 16. The fitting arrangement 12 is subsequently pivoted to a predetermined fitting position by means of the robot arm 14. In a further step of the blind riveting method, the blind rivet 22 is introduced with its sleeve-like portion 33 into the bore 24 until its rivet head 25 bears on the surface 27 of the first workpiece 26. Thereafter, by means of the blind riveting tool 16, a rivet shank 21 of the blind rivet 22 is drawn rearwards, so that an end 23, projecting out of the second workpiece 28, of the sleeve-like portion 33 of the blind rivet 22 expands radially and thus connects the two workpieces 26, 28 firmly to one another. The tensile force on the rivet shank 21 is increased until the latter breaks off at a predefined point 29. In this case, a shank residue remains in the fitted connection thus made, while the broken-off fraction of the rivet shank is disposed of in an automated way. The fitting arrangement 12 can subsequently be pivoted into the next fitting position by the robot 10.

Tolerances in the mounting of the blind riveting tool 16 or homing-in inaccuracies of the robot arm 14 may lead to an offset in position in an x-y plane parallel to the surface of the workpiece 26 (see the coordinate system illustrated in FIG. 1) and/or to an angular offset between the blind rivet 22 and the bore 24. To make a reliable riveted joint which, for example in cooperation with an adhesive material, can also assume a sealing-off function, however, it is necessary that the longitudinal axis of the blind rivet 22 is arranged centrally in the bore 24 and that the rivet head 25 of the blind rivet 22 lies flat on the surface 27 of the first workpiece 26.

For this reason, the fitting arrangement 12 has the compensating device 18 according to the invention which allows a deflecting movement of the blind riveting tool 16 (including the blind rivet 22) in relation to the housing 20 of the fitting arrangement 12. After the deflecting movement has been executed, the blind rivet 22 is positioned centrally in the bore 24 and is oriented axially parallel to a mid-axis 34 of the bore 24. A reliable riveted joint between the workpieces 26, 28 can consequently be made.

The compensating device 18 according to the invention will now be described in more detail. The compensating device 18 has a clamping arrangement 36 which is arranged between the blind riveting tool 16 and the housing 20 and which is designed to exert a controllable clamping force upon the blind riveting tool 16. Furthermore, the compensating device 18 has a load cell 38 which is designed to detect an essentially axial tensile force on the rivet shank during the fitting of the rivet 22.

Furthermore, the compensating device 18 has an angular position sensor 40 which detects an angular position of the blind riveting tool 16 in three-dimensional space.

Moreover, the compensating device 18 has a control unit 42 which is designed to activate the clamping arrangement 36 so that an adjustable clamping force is exerted upon the blind riveting tool 16.

The load cell 38 and the angular position sensor 40 are optional elements of the compensating device 18. However, in so far as these two elements (load cell 38/angular position sensor 40) are present, the control unit 42 can activate the clamping arrangement 36 as a function of the detected tensile force and/or of the detected angular position. Further alternative methods for activating the clamping arrangement 36 will be explained in connection with FIGS. 3 and 4.

FIGS. 2A-C illustrates an embodiment of the compensating device 18 according to the invention. In this case, with the aid of FIGS. 2A-C, mainly the mounting of the blind riveting tool 16 on the housing 20 by means of the compensating device 18 will be described. For the sake of clarity, therefore, the other elements of the compensating device 18 (such as, for example, the control unit 42) are not illustrated in FIG. 2.

As may be taken from FIG. 2A, the compensating device 18 has in this exemplary embodiment a rubber damper 44 which is secured to the housing 20 and on which the blind riveting tool 16 is mounted elastically. The rubber damper 44 relieves the clamping arrangement 36 of basic holding forces for holding the blind riveting tool 16. The clamping arrangement 36 can therefore be aimed essentially at setting a degree of freedom and the associated possibilities of movement of the blind riveting tool 16.

The clamping arrangement 36 has two controllable clamping units 46, 48 which are offset to one another in the axial direction 19 and which are designed in the present exemplary embodiment as bellows-type cylinders 46, 48. In this case, each of the bellows-type cylinders 46, 48 is loaded, by means of an actuator 47 not illustrated in FIG. 2A, with a pressure which is determined by the control unit 42. The bellows-type cylinders 46, 48 surround the blind riveting tool 16 in a circumferential direction transversely to the axial direction 19 and, at least in a completely filled state (see the initial state, illustrated in FIG. 2A, of the clamping arrangement 36), bear directly against the blind riveting tool 16. The blind riveting tool 16 is consequently secured essentially rigidly to the housing 20 and is oriented in the axial direction 19.

FIG. 2B shows a first compensating state of the compensating device 18. In this case, the first bellows-type cylinder 46 is at least partially depressurized (de-aerated). By the bellows-type cylinder 46 being depressurized, a first degree of freedom of the blind riveting tool 16 is set. In particular, the at least partially de-aerated bellows-type cylinder 46 makes it possible for the blind riveting tool 16 to execute a tilting movement (α) in relation to the axial direction 19. Compensation of an angular offset between the blind rivet 22 and the bore 24 can thus take place. Depending on the degree of emptying of the first bellows-type cylinder 46, moreover, the maximum possible tilting movement (α) can be determined.

FIG. 2C illustrates a second compensating state of the compensating device 18. In this state, both bellows-type cylinders 46, 48 are at least partially depressurized under the control of the control unit 42. Consequently, a second degree of freedom of the blind riveting tool 16 is set. In the second compensating state, therefore, a compensating movement in the lateral direction (β) perpendicularly to the axial direction 19 and a tilting movement (α) of the blind riveting tool 16 are made possible.

It will be appreciated that FIGS. 2B and 2C show merely two exemplary states and any other emptying states of the bellows-type cylinders 46, 48 can be set on the basis of activation by the control unit 42. Depending on the degree of emptying of the bellows-type cylinders 46, 48, the blind riveting tool 16 is mounted on the housing 20 in a more or less floating manner. By the controlled discharge of air from the bellows-type cylinders 46, 48, slow tolerance compensation of the blind riveting tool 16 can be brought about as a function of specific conditions (for example, a measured tensile force or deflecting force). Furthermore, during the emptying of the bellows-type cylinders 46, 48, the angular position detected by the angular position sensor 40 can also be taken into account. It is thus possible to compensate the dead weight of the blind riveting tool 16 in various positions of use of the latter (for example, horizontal orientation or “overhead” positioning of the blind riveting tool 16). What can thereby be achieved is that, for example, lateral displacement or tilting of the blind riveting tool 16 is based only on the actual offset in position/attitude of the blind rivet 22 with respect to the bore 24 and does not result from the dead weight from the blind riveting tool 16.

Various embodiments of the method according to the invention for the automated fitting of an element, in the present case the blind rivet 22, into the bore 24 of the workpieces 26, 28 will be explained by means of FIGS. 3 and 4. In this case, in the present instance, it will be assumed that the compensating device 18 is designed according to the embodiment illustrated in FIGS. 2A-C. It should be noted, however, that the method according to the invention can also be carried out with further embodiments of the compensating device 18.

FIG. 3 shows a first embodiment of the method 50 according to the invention.

In a step 52, the blind rivet 22 is positioned above the bore 24 of the workpieces 26, 28 by the robot 10. Owing to tolerances in the mounting of the blind riveting tool 16 on the housing 20 or else because of positioning inaccuracies of the robot 10, the blind rivet 22 may have an offset in position (offset in the x-y plane parallel to the surface of the workpieces 26, 28) and/or an offset in attitude (angular offset) in relation to the bore 24.

For this reason, in a step 54, the pressure in the rear bellows-type cylinder 46 is reduced, for example, to a fixed value stored in the control unit 42. A first degree of freedom of the blind riveting tool 16 is consequently set, in which tilting of the blind riveting tool 16 is made possible.

In a step 56, the blind rivet 22 is introduced into the bore 24. An offset in position/angular offset between the blind rivet 22 and the bore 24 can be compensated by the blind riveting tool 16 being tilted.

After the introduction of the blind rivet 22, in a step 58, the front bellows-type cylinder 48 is also depressurized or enabled and consequently a second degree of freedom of the blind riveting tool 16 is set. In this case, the pressure of the front bellows-type cylinder 48 can be reduced to a further fixed value stipulated by the control unit 42. After the second degree of freedom is set, the blind riveting tool 16 can both be tilted (α) and be moved laterally transversely (β) to the axial direction. This ensures that the blind rivet 22 can be oriented at right angles to the workpieces 26, 28 and that the rivet head 25 of the blind rivet 22 lies flat on the surface 27 of the workpiece 26.

Subsequently, in a step 60, the fitting (setting) process for fitting the blind rivet 22 into the bore 24 is carried out. For this purpose, a rivet shank 21 of the blind rivet 22 is surrounded by the blind riveting tool 16 and drawn rearwards until the rivet shank breaks off at a predefined point 29. As a result of the tensile force on the rivet shank, the blind rivet 22 expands radially at its end 23 projecting out of the workpiece 28 and thus, in cooperation with the rivet head 25 lying on the surface 27 of the workpiece 26, clamps the two workpieces 26, 28. By the second degree of freedom of the blind riveting tool 16 being set, the blind rivet 22 can be oriented axially parallel to the bore 24 during the fitting process. This makes it possible to produce a high-quality blind riveted joint.

As soon as the process of fitting the blind rivet 22 is concluded, the bellows-type cylinders 46, 48 are filled again in a step 62, in order to produce the initial state in the clamping arrangement 36. The blind riveting tool 16 is consequently secured essentially rigidly to the housing 20 and therefore secured mechanically during the pivoting of the robot arm 14 to the next fitting position.

Alternatively, the pressure in the cylinders 46, 48 can be increased slowly again even during the fitting process. As a result, in the event of an offset in position/attitude of the blind rivet 22, a force is exerted upon the robot arm 14. If the robot arm 14 is designed as what is known as a soft arm, the deflecting movement of the blind riveting tool 16 can be tracked by the robot arm 14. This tracking movement can be detected by the robot 10 and used to correct the position of the bore 24. This, in turn, results in an optimization of the next setting process for the blind rivet 22.

In the above-outlined first embodiment of the method 50 according to the invention, simple switching valves can be used for activating the bellows-type cylinders 46, 48. If proportional valves are used and the angular position is detected by means of the angular position sensor 40, the method 50 may be modified as follows.

In the step 54, the pressure in the rear bellows-type cylinder 46 is reduced to a position-dependent value, the pressure values for each angular position in space being stored in the control unit 42. The dead weight of the blind riveting tool 16 is thus compensated independently of the position of use of the fitting arrangement 12. In other words, the weight of the blind riveting tool 16 does not lead to tilting or lateral offsetting of the blind riveting tool 16 in relation to the housing 20. A deflecting movement of the blind riveting tool 16 takes place essentially only on account of the offset in position and/or angular offset of the blind rivet 22 in relation to the bore 24.

In a similar way to this, the step 58 may also be modified. Thus, the front bellows-type cylinder 48 is also enabled to a position-dependent pressure value. The blind riveting tool 16 is thereby put into a state in which the blind riveting tool 16 remains in position (compensation of the dead weight), but reacts to additional forces acting upon the blind riveting tool 16 from outside. The blind riveting tool 16 can thus be oriented at right angles to the workpieces 26, 28 during the fitting process.

In FIG. 4, a second embodiment of the method according to the invention is shown and is designated by 50′. Method steps of the second embodiment which correspond to the steps of the first embodiment are given the same reference numerals. Essentially the differences will be explained below.

After the blind rivet 22 has been introduced into the bore 24, in the present exemplary embodiment the fitting (setting) process is started in a step 60′. This means that the blind riveting tool 16 surrounds the rivet shank 21 of the blind rivet 22 and exerts a tensile force upon the rivet shank 21. The tensile force on the blind rivet 22 is in this case detected via the load cell 38. As soon as the measured tensile force overshoots a predetermined threshold value, the front bellows-type cylinder 48 is depressurized slowly as a function of the tensile force and the blind riveting tool 16 is consequently enabled. In principle, the time sequence of the fitting process can be followed via the detection of the tensile force. Thus, during the fitting process, the blind rivet 22 can be oriented at right angles to the component slowly and as a function of the time sequence of the setting process.

In a further variant of the method 50′, in the step 60′, additionally or alternatively a deflecting force (arrow ε) can be detected which, in particular, is oriented transversely to the axial direction 19 and which is exerted upon the blind rivet 22 by the workpieces 26, 28 during the fitting of the blind rivet 22 on account of an offset in position and/or angular offset between the blind rivet 22 and the bore 24. As soon as the measured deflecting force rises, the front bellows-type cylinder 48 is depressurized slowly as a function of the deflecting force, in order thereby to enable further possibilities of movement for the blind riveting tool 16. In so far as both the tensile force and the rivet shank and the deflecting force transversely to the axial direction 19 are detected, the control unit 42 sets the pressure in the bellows-type cylinders 46, 48 as a function of these two detected variables. In this variant of the method 50′, the deflecting forces actually occurring as a result of an offset in position/angular offset of the blind rivet 22 with respect to the bore 24 are taken into account in the activation of the bellows-type cylinders 46, 48. The blind rivet 22 can consequently be reliably oriented axially parallel to the bore 24 during the fitting process. The rivet head of the blind rivet 22 lies flat on the surface of the workpiece 26. This leads, in turn, to a high quality of the blind riveted joint made.

FIG. 5 shows an exemplary embodiment of a force detection unit 64 for detecting the deflecting force (arrow ε). The force detection unit 64 has in the present example three strain gauges 64 which are arranged between the blind riveting tool 16 and the housing 20. The strain gauges 64 are designed to detect a force (arrow ε) (deflecting force), oriented, in particular, transversely to the axial direction, between the blind riveting tool 16 and the housing 20. It will be appreciated that any other number of strain gauges 64 may also be used for measuring the deflecting force. Other sensors may likewise also be employed for determining this force.

FIGS. 6 to 9 show further embodiments of the compensating device 18 according to the invention.

In the exemplary embodiment illustrated in FIG. 6A, the compensating device 18 has a mechanical guide element 66 in the form of a plain or rolling bearing, on which the blind riveting tool 16 is mounted rotatably and/or displaceably. In this case, the mechanical guide element 66 is formed on the housing 20. In this embodiment of the compensating device 18, the rear bellows-type cylinder 46 allows tilting of the blind riveting tool 16 and a deflecting movement in the axial direction. By contrast, the front bellows-type cylinder 48 allows position compensation in the x-y plane, but only if the rear bellows-type cylinder 46 is likewise depressurized.

The set-up of the compensating device 18 from FIG. 6B corresponds essentially to that of the compensating device 18 from FIG. 6A. Owing to the different geometrical shape of the housing 20 and to the other arrangement of the bellows-type cylinders 46, 48 which is associated with this, simply other force conditions are generated during the securing or enabling of the blind riveting tool 16.

The compensating device 18 from FIG. 6C has a mechanical guide element 66 which is formed conically. On account of the conical hold of the guide element 66, essentially only a deflecting movement in the axial direction is enabled by the de-aeration of the rear bellows-type cylinder 46. With the aid of the front bellows-type cylinder 48, angular compensation and position compensation of the blind riveting tool 16 can be controlled when the bellows-type cylinder 46 is at least partially emptied.

The set-up of the compensating device 18 from FIG. 6D corresponds essentially to the set-up from FIG. 6C, the mounting of the blind riveting tool 16 on the housing 20 in the axial direction having been reversed. The functioning of the bellows-type cylinders 46, 48 is consequently also reversed, as compared with the exemplary embodiment from FIG. 6C.

In the exemplary embodiment in FIG. 6E, the compensating device 18 has, furthermore, an inner housing 68 which is arranged between the blind riveting tool 16 and the housing 20. In this case, the bellows-type cylinder 46 is arranged between the blind riveting tool 16 and the inner housing 68 and the bellows-type cylinder 48 is arranged between the inner housing 68 and the housing 20. The bellows-type cylinder 46 makes it possible, by de-aeration, to have a tilting movement of the blind riveting tool 16 and a deflecting movement of the blind riveting tool 16 in the axial direction 19. By the bellows-type cylinder 48 being depressurized, position compensation of the blind riveting tool 16 in the x-y plane can take place. Advantageously, in this embodiment, attitude compensation (angular compensation) and position compensation can be activated independently of one another.

The functioning of the compensating device 18 from FIG. 6F corresponds essentially to that from FIG. 6E. However, in this embodiment, the housing 20 has a narrowed inner region 70 which defines an end position for the position compensation of the blind riveting tool 16.

FIGS. 7A and 7B shows a further embodiment of the compensating device 18 according to the invention, an alternative clamping method for securing the blind riveting tool 16 being used here. FIG. 7A shows a top view of the compensating device 18 in the axial direction. In this embodiment, the clamping unit 46′ (instead of a bellows-type cylinder) has three clamping elements 72 which are arranged so as to be offset to one another in the circumferential direction of the blind riveting tool 16. In this case, the clamping elements 72 are designed in each case as an inflatable compressed-air hose 72. If, for example, only the compressed-air hose 72 illustrated on the left in FIG. 7A is depressurized, advantageously only the possibility of lateral deflection of the blind riveting tool 16 to the left (see FIG. 7A) can be enabled.

FIG. 7B shows a side view of the compensating device 18 from FIG. 7A. It can be gathered from this side view that the compensating device 18 likewise has in this embodiment two clamping units 46′, 48′ which, however, are constructed here in each case from three clamping elements 72. The basic functioning corresponds, however, to that of the exemplary embodiment from FIGS. 2A-C. In particular, the method explained with the aid of FIGS. 3 and 4 can also be applied to the embodiment of the compensating device 18 which is illustrated in FIGS. 7A-B.

The compensating devices of FIGS. 8 and 9 are comparable in terms of set-up to the embodiment of FIGS. 7A-B. Merely the compressed-air hoses 72 running in the axial direction 19 are replaced by clamping cylinders 72′ (see FIG. 8) or by cylinder-driven clamping jaws 72″ (see FIG. 9). Since the clamping jaws 72″ surround the blind riveting tool 16 in a specific portion of the circumference, the number of clamping elements 72′ can be reduced.

Although preferred embodiments of the compensating device 18 and of the method 50 have thus been shown, it will be appreciated that various changes and modifications can be made, without departing from the scope of the invention.

For example, the compensating device 18 according to the invention and the method 50 according to the invention can not only be employed in blind riveting, but can also be used for other fitting processes (for example, for stud welding).

The components of the compensating device 18 may likewise be arranged differently. For example, the control unit 42 may be a central control unit of the robot 10 which is arranged in a fixed main housing of the robot 10, not in the fitting arrangement 12.

Although exemplary embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents. 

What is claimed is:
 1. A compensating device for a tool for fitting an element into a hole of a workpiece, the tool mounted axially on a housing by the compensating device, the compensating device comprising: a clamping arrangement located between the tool and the housing, and including two clamping units operable, in an initial state of the clamping arrangement, to secure the tool rigidly to the housing and, in a compensating state of the clamping arrangement, to set different degrees of freedom of the tool, the degrees of freedom defining possibilities of movement of the tool; and a control unit operable to activate the clamping units.
 2. A compensating device according to claim 1, the clamping units arranged offset to one another along an axis of the tool.
 3. A compensating device according to claim 1, wherein at least one of the clamping units surrounds the tool in a circumferential direction transverse to an axis of the tool.
 4. A compensating device according to claim 1, wherein at least one of the clamping units includes a compressed-air hose.
 5. A compensating device according claim 1, wherein at least one of the clamping units includes a plurality of clamping elements arranged offset to one another in the circumferential direction.
 6. A compensating device according to claim 5, the plurality of clamping elements including one of a compressed-air hose and a clamping cylinder.
 7. A compensating device according to claim 1, and further comprising a rubber damper secured to the housing and on which the tool is mounted elastically to the housing.
 8. A compensating device according to claim 1, the compensating device further comprising an angular position transmitter operable to detect an angular position of the tool in three-dimensional space, the control unit coupled electrically to the angular position transmitter and operable to activate the clamping units on the basis of the angular position.
 9. A compensating device according to claim 1 and further comprising a first force detection unit for measuring an axial setting force exerted upon the element by the tool in order to set the element in the workpiece, the control unit coupled electrically to the first force detection unit and operable to activate the clamping units on the basis of the fitting force.
 10. A compensating device according to claim 1 and further comprising a second force detection unit arranged between the tool and the housing for detecting a deflecting force substantially transverse to an axis of the tool, and which deflecting force arises when the element is being fitted into the workpiece, and is exerted upon the element by the workpiece on account of an offset in position between the element and the hole, the control unit coupled electrically to the second force detection unit and operable to activate the clamping units on the basis of the deflecting force.
 11. A compensating device according to claim 1, wherein a maximum deflecting movement of the tool in the direction of the possibilities of movement is defined by the clamping units.
 12. A method for the automated fitting of an element into a hole of a workpiece with the aid of a tool mounted axially on a housing by a compensating device, the compensating device including a clamping arrangement with at least two controllable clamping units, and the fitting method comprising the steps of: setting of an initial state of the clamping arrangement so that the tool is secured rigidly to the housing; automated feeding of the tool to the hole; setting of a first degree of freedom for the tool unit by activating at least one of the clamping units; introducing the element into the hole; executing a setting process in order to set the element in the hole; and setting a second degree of freedom for the tool, different from the first degree of freedom, by activating at least one other of the clamping units before and/or during the fitting process, and the degrees of freedom defining possibilities of movement of the tool unit.
 13. A fitting method according to claim 12 and further comprising a step of: detecting an angular position of the tool in three-dimensional space, and the activating of the clamping units is carried out on the basis of the angular position.
 14. A fitting method according to claim 12, and further comprising a step of measuring a setting force, which is exerted upon the element by the tool in order to set the element, and the activating of the clamping units is carried out on the basis of the fitting force in order to set the possibilities of movement of the second degree of freedom.
 15. A fitting method according to claim 12 and further comprising a step of measuring a deflecting force transverse to the axial direction and which is exerted upon the element by the workpiece during the fitting of the element into the workpiece on account of an offset in position between the element and the hole, and the activating of the clamping units is carried out on the basis of the deflecting force in order to set the possibilities of movement of the second degree of freedom.
 16. A blind rivet setting tool for setting a rivet in a workpiece, the blind rivet setting tool comprising: a housing; a rivet tool for fitting the rivet into a hole of a workpiece, the rivet tool mounted axially to the housing, and a compensating device located between the rivet tool and the housing, and whereby the rivet tool is mounted to the housing, the compensating device including: a clamping arrangement further including two clamping units which are operable, in an initial state of the clamping arrangement, to secure the rivet tool rigidly to the housing and, in a compensating state of the clamping arrangement to set different degrees of freedom of the rivet tool, the degrees of freedom defining possibilities of movement of the rivet tool, and a control unit operable to activate the clamping units.
 17. A blind rivet setting tool according claim 16 and further comprising: a first force detection unit coupled electrically to the control unit and operable for measuring a setting force, which is exerted upon the blind rivet by the rivet tool in order to set the rivet, and the control unit activates the clamping units on the basis of the fitting force. 